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The width allocated to lanes for motorists, buses, trucks, bikes, and parked cars is a sensitive and crucial aspect of street design. Lane widths should be considered within the assemblage of a given street delineating space to serve all needs, including travel lanes, safety islands, bike lanes, and sidewalks.
Each lane width discussion should be informed by an understanding of the goals for traffic calming as well as making adequate space for larger vehicles, such as trucks and buses.
Lane widths of 10 feet are appropriate in urban areas and have a positive impact on a street’s safety without impacting traffic operations.
Travel lanes are striped to define the intended path of travel for vehicles along a corridor. Historically, wider travel lanes (11–13 feet) have been favored to create a more forgiving buffer to drivers, especially in high-speed environments where narrow lanes may feel uncomfortable or increase potential for side-swipe collisions.
Lane widths less than 12 feet have also historically been assumed to decrease traffic flow and capacity, a claim new research refutes.1
Appendix A-P, p. A152, Florida Department of Transportation (2007). Appendix A-P and Appendix Q. Conserve By Bicycle Program Study Final Report. Tallahassee, FL: FDOT.
The relationships between lane widths and vehicle speed is complicated by many factors, including time of day, the amount of traffic present, and even the age of the driver. Narrower streets help promote slower driving speeds which, in turn, reduce the severity of crashes. Narrower streets have other benefits as well, including reduced crossing distances, shorter signal cycles, less stormwater, and less construction material to build.
See Corner Radii
Ingrid Potts, Douglas W. Harwood, and Karen R. Richard, “Relationship of Lane Width to Safety on Urban and Suburban Arterials,” (paper presented at the TRB 86th Annual Meeting, Washington, D.C., January 21–25, 2007).
Relationship Between Lane Width and Speed, (Washington, D.C.: Parsons Transportation Group, 2003), 1–6.
Previous research has shown various estimates of relationship between lane width and travel speed. One account estimated that each additional foot of lane width related to a 2.9 mph increase in driver speed.
Kay Fitzpatrick, Paul Carlson, Marcus Brewer, and Mark Wooldridge, “Design Factors That Affect Driver Speed on Suburban Arterials": Transportation Research Record 1751 (2000):18–25.
Other references include:
Macdonald, Elizabeth, Rebecca Sanders and Paul Supawanich. The Effects of Transportation Corridors’ Roadside Design Features on User Behavior and Safety, and Their Contributions to Health, Environmental Quality, and Community Economic Vitality: a Literature Review. UCTC Research Paper No. 878. 2008.
Adapted from the Urban Street Design Guide, published by Island Press.